Field of the Invention
The embodiments of the invention generally relate to an aluminum substrate support suitable for use in high temperature semiconductor processing systems.
Background of the Related Art
Integrated circuits have evolved into complex devices that can include millions of transistors, capacitors and resistors on a single chip. The evolution of chip designs continually requires faster circuitry and greater circuit density that demand increasingly precise fabrication processes. One fabrication process frequently used is chemical vapor deposition (CVD).
Chemical vapor deposition is generally employed to deposit a thin film on a substrate, such as a semiconductor wafer. Chemical vapor deposition is generally accomplished by introducing a precursor gas in to a vacuum chamber. The precursor gas is typically directed through a showerhead situated near the top of the chamber. The precursor gas reacts to form a layer of material on a surface of the substrate that is positioned on a heated substrate support. Purge gas is routed through holes in the support to the edge of the substrate to prevent deposition at the substrate's edge that may cause the substrate to adhere to the support or flake off during processing. Volatile by-products produced during the reaction are pumped from the chamber through an exhaust system.
One material frequently formed on substrates using a chemical vapor deposition process is tungsten. A precursor gas that may be used to form tungsten generally includes tungsten hexafluoride (WF6) and silane. As the silane and tungsten hexafluoride mix, some “stray” tungsten (i.e., tungsten that does not deposit on the substrate) deposits on the showerhead and other chamber components. The stray tungsten film builds on the showerhead and may become a source of contamination in the chamber. Eventually, the stray tungsten may clog the holes in the showerhead that facilitate the passage of the precursor gas therethrough necessitating the showerhead be removed and cleaned or replaced. Chemical vapor deposition chambers also often require periodic cleaning after depositing other materials, for example dielectric materials such as SiO2.
To extend the interval in time between the routine maintenance of the showerhead, fluorine based chemistries are generally used to clean (i.e., etch away) the stray tungsten film. The fluorine base chemistry also reacts to form a layer of aluminum fluoride (AlFx) on the heated support that is commonly made of aluminum. The aluminum fluoride (AlFx) layer, if present in a controlled and uniform state, provides a protective coating and sacrificial layer over the heated support. However, if the aluminum fluoride (AlFx) growth becomes random or excessive between different areas of the heated support, the AlFx layer can become defect ridden, and/or form selectively at initiation sites that generate flakes and particles, thus detrimentally becoming a particle generation and contamination source.
Many conventional aluminum substrate supports are forgings or castings. Forging processes are difficult to control and, as such, forged substrate supports generally exhibit a wide range of material properties, such as a wide range of grain sizes. Casting processes can also exhibit control difficulties which can result in a wide range of material properties, such as a wide range of grain sizes. The inventors have discovered that forged and cast substrate supports exhibiting large grain sizes have poor aluminum fluoride (AlFx) performance, i.e., the aluminum fluoride (AlFx) film has large amounts of defects, high particle generation and, consequently, short service life. Thus, it would be beneficial to produce an aluminum heated substrate support having an advantageous grain size distribution that does enhance the performance of adhered aluminum fluoride (AlFx) films.
Moreover, the heater body and stem joint of the substrate support must be configured to enable the use of such heaters at high temperatures. As the substrate support may be utilized at process temperatures ranging upward of 400 to 480 degrees Celsius, which is well in excess of recommended aluminum operational temperatures. Weld cracking may promote failure of the adhered aluminum fluoride (AlFx) films, along with vacuum leakage problems.
Therefore, there is a need in the art for an improved heated support suitable for use in chemical vapor deposition processes.